The field of rapid prototyping involves the production of prototype articles and small quantities of functional parts, as well as structural ceramics and ceramic shell molds for metal casting, directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective laser sintering process and a liquid binder three dimensional printing process. These techniques are similar, to the extent that they both use layering techniques to build three-dimensional articles. Both methods form successive thin cross-sections of the desired article. The individual cross-sections are formed by bonding together adjacent grains of a granular, i.e. particulate material on a generally planar surface of a bed of the granular material. Each layer is bonded to a previously formed layer to form the desired three-dimensional article at the same time as the grains of each layer are bonded together. The laser-sintering and liquid binder techniques are advantageous, because they create parts directly from computer-generated design data and can produce parts having complex geometries. Moreover, three dimensional printing can be quicker and less expensive than machining of prototype parts or production of cast or molded parts by conventional “hard” or “soft” tooling techniques, that can take from a few weeks to several months, depending on the complexity of the item.
An early three dimensional printing technique, described in U.S. Pat. No. 5,204,055, incorporated herein by reference in its entirety, describes the use of an ink-jet style printing head to deliver a liquid or colloidal binder material to sequentially applied layers of powdered material. The three-dimensional ink-jet printing technique or liquid binder method involves applying a layer of a powdered material to a surface using a counter-roller. After the powdered material is applied to the surface, the ink-jet printhead delivers a liquid binder in a predetermined pattern to the layer of powder. The binder infiltrates into gaps in the powder material and hardens to bond the powder material into a solidified layer. The hardened binder also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the previous steps are repeated, building successive cross-sectional portions until the final article is formed. Optionally, an adhesive can be suspended in a carrier that evaporates, leaving the hardened adhesive behind. The powdered material may be ceramic, metal, plastic or a composite material, and may also include fibers. The liquid binder material may be organic or inorganic. Typical organic binder materials used are polymeric resins or ceramic precursors, such as polycarbosilazane. Inorganic binders are used where the binder is incorporated into the final articles; silica is typically used in such an application.
As described in U.S. Pat. No. 6,007,318, incorporated herein by reference in its entirety, printed articles may be dipped or painted with a solution that infiltrates the article by capillary actions. This processing may improve handling properties of the article and prevent its decay.
The use of an absorbent filler to facilitate infiltrant absorption is described in U.S. Patent Application 2005/0059757, incorporated herein by reference in its entirety. That application describes the incorporation of thermoplastic fillers in a powder, with the activating or infiltration material being a solvent.